/Engine/Source/Runtime/Engine/Public/BoneContainer.h
Returns whether or not the skeleton index is contained in the mapping used to build this container. Note that even if the skeleton index is valid, it might not contain a valid compact pose index if that bone isn't used due to LOD or other reasons.
bool IsSkeletonPoseIndexValid ( const [FSkeletonPoseBoneIndex](API\Runtime\AnimationCore\FSkeletonPoseBoneIndex) & SkeletonIndex ) const